As everyone must have experienced, it is difficult to recognize steps when climbing stairs in the dark and the consequence could be serious if you miss a step. The conventional way to improve the safety is to install a luminaire inside a recession of the side wall of a step, so that the top surface of the lower step can be illuminated. However, the vision difference caused by the illuminated top surface of a lower step and the un-illuminated side surface of an upper step, and the uncomfortable light distribution still would cause trouble to passers. See FIG. 1, which shows an outdoors step luminaire with the conventional structure. In addition, another shortcoming of the conventional way lies in the necessity of opening a recession on the side surface of steps, which in turn costs a lot and complicates installation.
Unlike the conventional way described above, U.S. Pat. No. 5,430,627 proposed another lighting fixture with dual-channel units and without the need of opening a recession for purpose of illuminating both a step tread and a step riser. As a cross-section view of the disclosed device, FIG. 2 shows that channel 29 and channel 35 are provided to accommodate two light strings in order to illuminate the top edge and the base of a step, respectively. However, one problem with this type of device is that to simultaneously illuminate the top edge and base of a step, two sets of separate light strings have to be provided, which correspondingly need extra structure and therefore make the device large and complex. Another problem with this type of device is that since there is no light distribution design, as the conventional way above does, the luminance level on the top surface is not uniform; what is worse is that the light distribution for illuminating the top edge of a step will also emit upward to passers' eyes, which is undesirable.
It is an object of the invention to provide an optical device that can be used in a lighting device in order to at least reduce some of the aforementioned drawbacks.